Le 21/04/2013 19:22, Brendan Eich a écrit :
At JQueryUK, I threw up a sketch in slides based on
http://wiki.ecmascript.org/doku.php?id=strawman:relationships:
|class SkinnedMesh extends THREE.Mesh{
private identityMatrix,
bones,
boneMatrices;
constructor(geometry, materials) {
super(geometry, materials);
this@identityMatrix= new THREE.Matrix4();
this@bones= [];
this@boneMatrices= [];
...
}
...
}|
Can you provide more details on the semantics of syntax given the
relationship strawman?
With my understanding of the current proposal:
* in "this@bones = [];", 'bones' has to be a string or (unique) symbol.
I imagine the private syntax makes it a symbol (that will not be access
beyond the class scope) for the sake of non-forgeability.
* by default, objects have no value for @geti nor @seti [1], so
following the strawman, "this@bones = [];" should set the value for the
symbol. Unfortunately, (unique) symbols are enumerated via reflection,
so this is not private.
Sharing my thoughts trying to figure out the semantics you want to provide:
Was it implicit that each class declaration creates a @geti/@seti pair
as I describe at [2] and attach it to SkinnedMesh.prototype?
Hmm... if the pair on the prototype, then it can be shadowed by an
outsider via Object.defineProperty. I believe this shadowing will give
access to the symbol that was supposed to remain encapsulated any time
the @-syntax is used and break privacy. So no prototype.
So the last chance is for the class @geti/@seti pair to be assigned as
own property to each instances. And preferably make them
non-configurable/non-writable properties so they remain where they are.
One pair of property per instance may have a cost, but it sounds
possible to heavily optimize in memory frozen properties of the same
class for the 80% use case.
Even as own property, I believe inheritance can be made worked out (a
class extending another accesses the inherited class @geti/@seti pair
and builds its own pair on top of that. Well-encapsulated symbols won't
collide from one class to another).
Was it what you had in mind?
|class Point{
constructor(private x, private y) {}
add(other) {
return Point(this@x + other@x, this@y + other@y);
}
...
}
|
I'm guessing explanations to the above will lighten up my understanding
of this part, but in case there is something non-trivial to explain
here, I'll take it too.
Thanks,
David
[1] Last answer to Tom of
https://mail.mozilla.org/pipermail/es-discuss/2013-April/029697.html
[2] Last answer to Tom of
https://mail.mozilla.org/pipermail/es-discuss/2013-April/029700.html
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